Large of portions having a fixed color tone, so called screen tint portions, exist in color printed matters. The pre-press process of such screen tint portions are carried out by a special process different from the pre-press process of general color portions. Colors represented by a mixture of four colors of yellow (Y), magenta (M), cyan (C) and black (K) are given to respective screen tint portions. Such mixed colors are determined by numeric values expressed by dot percent rates (hereinafter called dot percent) in color separation used for respective colors at the time of printing. In the prior art, several kinds of masks for extracting the same dot percent regions and transparent films (screen tints) in which dots are provided at a desired dot percent rate are prepared to repeatedly expose light onto an exposure film to thereby carry out work for preparing a screen tint film.
In recent years, there have proposed technologies for preparing such a screen tint film by making use of a computer. For example, apparatus for preparing a screen tint film using a computer are disclosed in the specification of the Japanese Patent Application No. 213259/85, the specification of the Japanese Patent Application No. 270501/85, and the specification of the Japanese Patent Application No. 231365/87. In these apparatus, a contour line pictorial image described or depicted on a block copy is read by a scanner, etc. to carry out coloring process by a computer on the basis of the pictorial image data thus read to directly prepare screen tint films for respective colors.
The above-described apparatus for preparing a screen tint film using a computer typically include a disk unit as an external storage unit to retain pictorial image data in the disk unit. In the case of carrying out a pictorial image processing, such as coloring, pictorial image data in the disk unit is read out into the main memory in the computer to implement a pictorial image processing, such as coloring, to the pictorial image data in the main memory. During implementation of such pictorial image processing, it is necessary to display a pictorial image subject to processing on a visual display. For affecting such display, a frame memory is provided to transfer pictorial image data required for display from the main memory to the frame memory to thereby display a necessary pictorial image.
Ordinarily, the pictorial image data include raster data comprising color values of respective pixels arranged in order of arrangement of the pixels, and runlength data indicating arrangement of pixels having the same color value. In the conventional apparatus, the main memory and the frame memory store pictorial image data in the form of raster data, and the disk unit stores pictorial image data in the form of runlength data. This is because since the frame memory is directly connected to the visual display, it is necessary to retain data in the form of raster data, whereas it is convenient to retain data in the disk unit for storing several pictorial images in the form of runlength data permitting the whole capacity of data to be less. In the main memory for transferring data to the frame memory, an approach is used to retain data in the form of raster data in the same manner as in the case of the frame memory. Accordingly, in the conventional apparatus, pictorial image data in the form of runlength data in the disk unit is converted to raster data and is then read out onto the main memory. The raster data on the main memory is transferred to the frame memory in the form of raster data as it is, thus displaying pictorial images.
However, such apparatus have the problem that an extremely large capacity main memory is required. As previously described, since raster data requires the same number of data as the number of all pixels, a memory for storing massive data content is required in the case of a pictorial image having high resolution. Since the main memory of a computer generally is very expensive per bit compared to a disk, etc., there is the problem that if a main memory having a large capacity is required, the cost of the apparatus is greatly increased.
Another problem with the conventional apparatus is that, in the case of displaying a pictorial image in an expanded or contracted manner, or in the case of implementing coloring processing to pictorial image, the computational or operational efficiency is very poor, resulting in a prolonged computational or operational time. The expansion/contraction processing or the coloring processing is implemented to pictorial image data in the main memory. As previously described, since the main memory retains pictorial image data in the form of raster data in the conventional apparatus, various computational processing are implemented on the raster data. Implementation of computational processing on such a massive volume of raster data is a very inefficient and requires much processing time. In addition, the same problem arises also with respect to the computation in the case of draw processing in order to modify a pictorial image.
A first object of this invention is to provide a pictorial image processing system capable of reducing cost by lowering the capacity of the main memory, and capable of performing highly efficient computational processing.
Generally, in the apparatus for preparing a screen tint film, an operator carries out coloring processing on the basis of a color instruction while displaying a pictorial image on a visual display screen. For this reason, a work for designating an area or region subject to processing is required. In the conventional apparatus, an approach is employed to designate a rectangle on a display screen or designate a closed area encompassed by a predetermined contour line thereon to represent the area subject to processing.
However, an area designation method in the above-described apparatus for preparing a screen tint film has not necessarily good operability for an operator. For example, in the case of carrying out an area designation with respect to a very complicated pattern, designation of a rectangular area cannot result in a sufficient area designation. Further, in the case of designating a closed area encompassed by a contour line, if there is a break in the contour line, designation as a closed area cannot be made.
A second object of this invention is to provide a method of inputting a polygon, which is capable of improving operability of such an area designation.
Further, the conventional apparatus for preparing a screen tint film has the problem that the working efficiency at the time of modification and coloring works is low. In conventionally proposed apparatus, a desired pattern can be displayed on a visual display screen with a desired magnification. However, since the entire display of the display unit is switched to that of a new picture every time expanding display and/or contracting display are carried out, only one pattern having a predetermined magnification can be displayed within one screen. Accordingly, an operator cannot grasp the entire image of that pattern when an expanding display is conducted, and cannot observe a line drawing of a fine portion when a contracting display is conducted.
A third object of this invention is to provide a pictorial processing system capable of displaying, in the form of a multi-window, several patterns with desired magnifications within one screen, respectively.